A radiographic camera such as the Anger camera disclosed in the U.S. Pat. No. 3,011,057 which issued in the name of H. O. Anger on Nov. 28, 1961 and in the U.S. Pat. No. 3,914,611 which issued in the name of K. J. Stout on Oct. 21, 1975, is often utilized for obtaining a radiographic image of a radioactive subject. Such a camera includes a scintillator viewed by a set of scintillation detectors or photomultiplier tubes providing signals which are combined, typically, by a resistor matrix to provide a Z-axis signal which signals the presence of a radioactive event in the subject. Resistor matrices also combine the detector signals to provide coordinate axes signals, Cartesian coordinates having X and Y signals being readily implemented, to serve as an address for locating the radioactive event.
A problem arises in that the many photomultiplier tubes utilized in present day cameras are subject to individual drifting which varies the locations and, hence, the density of the apparent locations of the radioactive events as provided by the coordinate axes signals. Regions of increased event density in the image of the subject appear to a clinician viewing the image as regions of greater intensity. As a result, a clinican viewing the image produced by the camera perceives regions of varying intensity which may be incorrectly diagnosed as a tumor or malady.